Once the patient’s ABO type and RhD type are confirmed, the patient can be categorized as A-positive, O-negative, and so forth. This is sufficient information to avoid acute hemolytic transfusion reactions from the transfusion of ABO-incompatible blood, and to avoid RhD sensitization. However, it will not prevent less severe forms of hemolysis due to incompatibility against minor blood type antigens. For this, it is also necessary to regularly screen a transfusion recipient’s plasma for antibodies against these antigens.
The antibody screen is a series of indirect antiglobulin tests between the patient’s plasma and two or three screening cells that collectively express the antigens to which common and clinically significant antibodies are found. Additional details regarding available testing methodologies can be found in the supplemental information section of this document.
If an antibody screen is positive, an antibody investigation is required to characterize the specificity of the responsible antibodies. In an investigation, indirect antiglobulin tests are performed against a larger array of reagent red cells. In straightforward cases, a standardized panel of 12 cells (including the patient’s own RBCs, or “autocontrol”) is sufficient to confirm the specificity of any antibodies detected by screening. In complex cases, however, multiple and customized panels may be required.
Details on antibody investigation will be discussed in Module 4 of this series.
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